1. Field of The Invention
This invention relates to a display device and more particularly, to a gas discharge-type display panel wherein patterns such as letters, figures and the like are displayed by utilization of gas discharge.
2. Description of The Prior Art
Cathodes of known gas discharge-type display panels are formed by screen printing a Ni paste on a glass substrate and firing the printed paste in air. Since the Ni paste can be readily fired in air, the formation is very easy. However, the Ni cathode is relatively high in firing potential and minimum discharge keeping potential and, thus, Ni is not necessarily satisfactory as a material for the cathode. In addition, when the discharge takes place, the Ni cathode is sputtered by the action of generated ions and is deposited on a front glass substrate on which an anode has been formed, with a lowering of light transmission and a reduction of brightness. This will shorten the life of the display panel. To solve the problem involved in the prior art display panels, attempts have been made to fabricate a cathode with a double-layer structure. In the cathode, Ni is provided as an underlying electrode on which a paste of a mixture of LaB.sub.6 having a small work function and a small amount of alkali glass is screen printed and fired. This type of cathode is described, for example, in Technical Report IPD59-10 (1981) from the Television Society.
LaB.sub.6 has a work function of 2.66 eV, which is smaller than 5.24 eV of the work function of Ni. If a cathode based on such a small work function can be formed, the resultant gas discharge-type display panel will have low firing potential and low minimum discharge keeping potential. However, LaB.sub.6 is liable to form an oxide layer on the surface thereof. When LaB.sub.6 is divided into fine particles having several micrometers in size, the area of the oxide layer increases with an increasing surface area. The total electric conductivity is eventually lowered considerably. Thus, the inherent characteristic of the LaB.sub.6 cannot be developed when used in the form of fine particles.
In order to reduce the production costs of the panel, it is usual to employ soda glass as the substrate. The cathode is formed by a screen printing technique which is adapted for mass production. The printed layer is then fired in air. This inevitably involves oxidation of at least a part of LaB.sub.6. As a result, the electric conductivity of the layer is lowered by not less than three orders of magnitude than the conductivity of LaB.sub.6. This leads to the problem that the firing potential and the minimum discharge keeping potential become high and unstable.
To avoid the above problem, attempts have been made to fire in an inert gas such as argon, nitrogen or the like. The firing in an inert gas is effective when the particles of LaB.sub.6 have a size of not smaller than several tens micrometers. However, little effect will not be expected when the particle size is as small as several micrometers or below.